Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
CURRENT ASSETS:
Allowance for accounts receivable	$ 309	$ 426
Preferred stock
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Shares issued (in shares)	0	0
Shares outstanding (in shares)	0	0
Class A
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	750,000,000	750,000,000
Common stock, shares issued (in shares)	89,768,000	55,218,000
Common stock, shares outstanding (in shares)	89,768,000	55,218,000
Class B
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	151,047,000	148,481,000
Common stock, shares outstanding (in shares)	151,047,000	148,481,000
Class C
Common stock
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	75,000,000	75,000,000
Common stock, shares issued (in shares)	0	42,945,000
Common stock, shares outstanding (in shares)	0	42,945,000